For an average size city, it has been esimated that up to one million dollars per year of revenue may be lost due to theft from parking meters. Although some thefts are isolated incidents, most of the revenue loss is incurred as a result of systematic theft. Systematic parking meter theft may occur when a person steals a parking meter itself, such as by removing the head of the meter. The parking meter head can then be used to make a master key that is capable of opening other parking meters. Prior attempts to design locks that cannot be reverse engineered have generally been unsuccessful. As a result, there is a long-felt need to a lock system for parking meters and other receiving devices that render such devices immune to systematic theft.